add SPICE_MSG_MAIN_AGENT_CONNECTED_TOKENS

Similarly to SPICE_MSG_AGENT_CONNECTED, the msg notifies the main
channel about attaching an agent. In addition the msg also contains the
number of tokens allocated to the client.

spice/enums.h

@@ -414,6 +414,7 @@ enum {
     SPICE_MSG_MAIN_MIGRATE_END,
     SPICE_MSG_MAIN_NAME,
     SPICE_MSG_MAIN_UUID,
+    SPICE_MSG_MAIN_AGENT_CONNECTED_TOKENS,
 
     SPICE_MSG_END_MAIN
 };

spice/protocol.h

@@ -120,6 +120,7 @@ enum {
 enum {
     SPICE_MAIN_CAP_SEMI_SEAMLESS_MIGRATE,
     SPICE_MAIN_CAP_NAME_AND_UUID,
+    SPICE_MAIN_CAP_AGENT_CONNECTED_TOKENS,
 };
 
 enum {